Django2.0手册:Middleware



This document explains all middleware components that come with Django. For
information on how to use them and how to write your own middleware, see
the middleware usage guide.

Available middleware¶

Cache middleware¶

class UpdateCacheMiddleware[source]
class FetchFromCacheMiddleware[source]

Enable the site-wide cache. If these are enabled, each Django-powered page will
be cached for as long as the CACHE_MIDDLEWARE_SECONDS setting
defines. See the cache documentation.

“Common” middleware¶

class CommonMiddleware[source]

Adds a few conveniences for perfectionists:

  • Forbids access to user agents in the DISALLOWED_USER_AGENTS
    setting, which should be a list of compiled regular expression objects.

  • Performs URL rewriting based on the APPEND_SLASH and
    PREPEND_WWW settings.

    If APPEND_SLASH is True and the initial URL doesn’t end
    with a slash, and it is not found in the URLconf, then a new URL is
    formed by appending a slash at the end. If this new URL is found in the
    URLconf, then Django redirects the request to this new URL. Otherwise,
    the initial URL is processed as usual.

    For example, foo.com/bar will be redirected to foo.com/bar/ if
    you don’t have a valid URL pattern for foo.com/bar but do have a
    valid pattern for foo.com/bar/.

    If PREPEND_WWW is True, URLs that lack a leading “www.”
    will be redirected to the same URL with a leading “www.”

    Both of these options are meant to normalize URLs. The philosophy is that
    each URL should exist in one, and only one, place. Technically a URL
    foo.com/bar is distinct from foo.com/bar/ — a search-engine
    indexer would treat them as separate URLs — so it’s best practice to
    normalize URLs.

  • Handles ETags based on the USE_ETAGS setting. If
    USE_ETAGS is set to True, Django will calculate an ETag
    for each request by MD5-hashing the page content, and it’ll take care of
    sending Not Modified responses, if appropriate.

  • Sets the Content-Length header for non-streaming responses.

Changed in Django 1.11:

Older versions didn’t set the Content-Length header.

Deprecated since version 1.11: The USE_ETAGS setting is deprecated in favor of using
ConditionalGetMiddleware for ETag
processing.

CommonMiddleware.response_redirect_class

Defaults to HttpResponsePermanentRedirect. Subclass
CommonMiddleware and override the attribute to customize the redirects
issued by the middleware.

class BrokenLinkEmailsMiddleware[source]

GZip middleware¶

class GZipMiddleware[source]

Warning

Security researchers recently revealed that when compression techniques
(including GZipMiddleware) are used on a website, the site may become
exposed to a number of possible attacks. Before using GZipMiddleware on
your site, you should consider very carefully whether you are subject to
these attacks. If you’re in any doubt about whether you’re affected, you
should avoid using GZipMiddleware. For more details, see the the BREACH
paper (PDF)
and breachattack.com.

Compresses content for browsers that understand GZip compression (all modern
browsers).

This middleware should be placed before any other middleware that need to
read or write the response body so that compression happens afterward.

It will NOT compress content if any of the following are true:

  • The content body is less than 200 bytes long.
  • The response has already set the Content-Encoding header.
  • The request (the browser) hasn’t sent an Accept-Encoding header
    containing gzip.

If the response has an ETag header, the ETag is made weak to comply with
RFC 7232#section-2.1.

You can apply GZip compression to individual views using the
gzip_page() decorator.

Conditional GET middleware¶

class ConditionalGetMiddleware[source]

Handles conditional GET operations. If the response doesn’t have an ETag
header, the middleware adds one if needed. If the response has a ETag or
Last-Modified header, and the request has If-None-Match or
If-Modified-Since, the response is replaced by an
HttpResponseNotModified.

Changed in Django 1.11:

In older versions, the middleware set the Content-Length and Date
headers and didn’t set the ETag header.

Locale middleware¶

class LocaleMiddleware[source]

Enables language selection based on data from the request. It customizes
content for each user. See the internationalization documentation.

LocaleMiddleware.response_redirect_class

Defaults to HttpResponseRedirect. Subclass
LocaleMiddleware and override the attribute to customize the redirects
issued by the middleware.

Message middleware¶

class MessageMiddleware[source]

Enables cookie- and session-based message support. See the
messages documentation.

Security middleware¶

Warning

If your deployment situation allows, it’s usually a good idea to have your
front-end Web server perform the functionality provided by the
SecurityMiddleware. That way, if there are requests that aren’t served
by Django (such as static media or user-uploaded files), they will have
the same protections as requests to your Django application.

class SecurityMiddleware[source]

The django.middleware.security.SecurityMiddleware provides several security
enhancements to the request/response cycle. Each one can be independently
enabled or disabled with a setting.

HTTP Strict Transport Security

For sites that should only be accessed over HTTPS, you can instruct modern
browsers to refuse to connect to your domain name via an insecure connection
(for a given period of time) by setting the “Strict-Transport-Security”
header
. This reduces your exposure to some SSL-stripping man-in-the-middle
(MITM) attacks.

SecurityMiddleware will set this header for you on all HTTPS responses if
you set the SECURE_HSTS_SECONDS setting to a non-zero integer value.

When enabling HSTS, it’s a good idea to first use a small value for testing,
for example, SECURE_HSTS_SECONDS = 3600 for one
hour. Each time a Web browser sees the HSTS header from your site, it will
refuse to communicate non-securely (using HTTP) with your domain for the given
period of time. Once you confirm that all assets are served securely on your
site (i.e. HSTS didn’t break anything), it’s a good idea to increase this value
so that infrequent visitors will be protected (31536000 seconds, i.e. 1 year,
is common).

Additionally, if you set the SECURE_HSTS_INCLUDE_SUBDOMAINS setting
to True, SecurityMiddleware will add the includeSubDomains directive
to the Strict-Transport-Security header. This is recommended (assuming all
subdomains are served exclusively using HTTPS), otherwise your site may still
be vulnerable via an insecure connection to a subdomain.

If you wish to submit your site to the browser preload list, set the
SECURE_HSTS_PRELOAD setting to True. That appends the
preload directive to the Strict-Transport-Security header.

Warning

The HSTS policy applies to your entire domain, not just the URL of the
response that you set the header on. Therefore, you should only use it if
your entire domain is served via HTTPS only.

Browsers properly respecting the HSTS header will refuse to allow users to
bypass warnings and connect to a site with an expired, self-signed, or
otherwise invalid SSL certificate. If you use HSTS, make sure your
certificates are in good shape and stay that way!

Note

If you are deployed behind a load-balancer or reverse-proxy server, and the
Strict-Transport-Security header is not being added to your responses,
it may be because Django doesn’t realize that it’s on a secure connection;
you may need to set the SECURE_PROXY_SSL_HEADER setting.

X-Content-Type-Options: nosniff

Some browsers will try to guess the content types of the assets that they
fetch, overriding the Content-Type header. While this can help display
sites with improperly configured servers, it can also pose a security
risk.

If your site serves user-uploaded files, a malicious user could upload a
specially-crafted file that would be interpreted as HTML or JavaScript by
the browser when you expected it to be something harmless.

To prevent the browser from guessing the content type and force it to
always use the type provided in the Content-Type header, you can pass
the X-Content-Type-Options: nosniff header. SecurityMiddleware will
do this for all responses if the SECURE_CONTENT_TYPE_NOSNIFF setting
is True.

Note that in most deployment situations where Django isn’t involved in serving
user-uploaded files, this setting won’t help you. For example, if your
MEDIA_URL is served directly by your front-end Web server (nginx,
Apache, etc.) then you’d want to set this header there. On the other hand, if
you are using Django to do something like require authorization in order to
download files and you cannot set the header using your Web server, this
setting will be useful.

X-XSS-Protection: 1; mode=block

Some browsers have the ability to block content that appears to be an XSS
attack
. They work by looking for JavaScript content in the GET or POST
parameters of a page. If the JavaScript is replayed in the server’s response,
the page is blocked from rendering and an error page is shown instead.

The X-XSS-Protection header is used to control the operation of the
XSS filter.

To enable the XSS filter in the browser, and force it to always block
suspected XSS attacks, you can pass the X-XSS-Protection: 1; mode=block
header. SecurityMiddleware will do this for all responses if the
SECURE_BROWSER_XSS_FILTER setting is True.

Warning

The browser XSS filter is a useful defense measure, but must not be
relied upon exclusively. It cannot detect all XSS attacks and not all
browsers support the header. Ensure you are still validating and
sanitizing
all input to prevent XSS attacks.

SSL Redirect

If your site offers both HTTP and HTTPS connections, most users will end up
with an unsecured connection by default. For best security, you should redirect
all HTTP connections to HTTPS.

If you set the SECURE_SSL_REDIRECT setting to True,
SecurityMiddleware will permanently (HTTP 301) redirect all HTTP
connections to HTTPS.

Note

For performance reasons, it’s preferable to do these redirects outside of
Django, in a front-end load balancer or reverse-proxy server such as
nginx. SECURE_SSL_REDIRECT is intended for the deployment
situations where this isn’t an option.

If the SECURE_SSL_HOST setting has a value, all redirects will be
sent to that host instead of the originally-requested host.

If there are a few pages on your site that should be available over HTTP, and
not redirected to HTTPS, you can list regular expressions to match those URLs
in the SECURE_REDIRECT_EXEMPT setting.

Note

If you are deployed behind a load-balancer or reverse-proxy server and
Django can’t seem to tell when a request actually is already secure, you
may need to set the SECURE_PROXY_SSL_HEADER setting.

Session middleware¶

class SessionMiddleware[source]

Enables session support. See the session documentation.

Site middleware¶

class CurrentSiteMiddleware[source]

Adds the site attribute representing the current site to every incoming
HttpRequest object. See the sites documentation.

Authentication middleware¶

class AuthenticationMiddleware

Adds the user attribute, representing the currently-logged-in user, to
every incoming HttpRequest object. See Authentication in Web requests.

class RemoteUserMiddleware

Middleware for utilizing Web server provided authentication. See
使用 REMOTE_USER 进行身份验证 for usage details.

class PersistentRemoteUserMiddleware

Middleware for utilizing Web server provided authentication when enabled only
on the login page. See 仅在登录界面使用 REMOTE_USER for usage
details.

CSRF protection middleware¶

class CsrfViewMiddleware[source]

Adds protection against Cross Site Request Forgeries by adding hidden form
fields to POST forms and checking requests for the correct value. See the
Cross Site Request Forgery protection documentation.

X-Frame-Options middleware¶

class XFrameOptionsMiddleware[source]

Simple clickjacking protection via the X-Frame-Options header.

Middleware ordering¶

Here are some hints about the ordering of various Django middleware classes:

  1. SecurityMiddleware

    It should go near the top of the list if you’re going to turn on the SSL
    redirect as that avoids running through a bunch of other unnecessary
    middleware.

  2. UpdateCacheMiddleware

    Before those that modify the Vary header (SessionMiddleware,
    GZipMiddleware, LocaleMiddleware).

  3. GZipMiddleware

    Before any middleware that may change or use the response body.

    After UpdateCacheMiddleware: Modifies Vary header.

  4. ConditionalGetMiddleware

    Before CommonMiddleware: uses its ETag header when
    USE_ETAGS = True.

  5. SessionMiddleware

    After UpdateCacheMiddleware: Modifies Vary header.

  6. LocaleMiddleware

    One of the topmost, after SessionMiddleware (uses session data) and
    UpdateCacheMiddleware (modifies Vary header).

  7. CommonMiddleware

    Before any middleware that may change the response (it sets the ETag and
    Content-Length headers). A middleware that appears before
    CommonMiddleware and changes the response must reset the headers.

    After GZipMiddleware so it won’t calculate an ETag header on gzipped
    contents.

    Close to the top: it redirects when APPEND_SLASH or
    PREPEND_WWW are set to True.

  8. CsrfViewMiddleware

    Before any view middleware that assumes that CSRF attacks have been dealt
    with.

    It must come after SessionMiddleware if you’re using
    CSRF_USE_SESSIONS.

  9. AuthenticationMiddleware

    After SessionMiddleware: uses session storage.

  10. MessageMiddleware

    After SessionMiddleware: can use session-based storage.

  11. FetchFromCacheMiddleware

    After any middleware that modifies the Vary header: that header is used
    to pick a value for the cache hash-key.

  12. FlatpageFallbackMiddleware

    Should be near the bottom as it’s a last-resort type of middleware.

  13. RedirectFallbackMiddleware

    Should be near the bottom as it’s a last-resort type of middleware.